1. Field of the Invention
This invention relates generally to fetal monitoring apparatuses and, more particularly, to an apparatus for sensing uterine activity, in particular, contractions.
2. Description of the Prior Art
Fetal monitors, which are typically quite sophisticated, are widely used to monitor the uterine activity of pregnant women, as well as the condition of the fetus and the uterus. Analysis of uterine contractions, in conjunction with fetal heart rate, during the pregnancy and labor yields significant information concerning the condition of the fetus as well as the advancement of labor. Such monitoring is particularly helpful in so-called difficult pregnancies to systematically evaluate fetal stress, but it is certainly of use in more routine pregnancies as well.
Information of fetal distress will result in prompt remedial action, including a cesarean delivery, both during pregnancy and/or during actual labor. Likewise, early contractions can be treated so as to achieve full-term pregnancies. Examples of currently available fetal monitors include the FetaScan from International Biomedics, Inc., the Corometrics 115 and the Hewlett-Packard 8040A.
Such fetal monitors, however, regardless of their sophistication, require a device or element to actually sense the uterine contractions.
These elements can be intra-uterine or extra-uterine. An example of an intra-uterine sensing element is a catheter which is capable of measuring uterine activity within the uterine cavity itself. Such sensors are disclosed in U.S. Pat. Nos. 4,785,822; 4,873,986; 4,873,990; 4,909,263; 4,942,882; 4,944,307; 4,953,563 and 4,966,161. However, these devices are invasive. Further, they cannot be used for pre-term monitoring because they are invasive.
Other devices, known as tocotonometers, are capable of non-invasively sensing uterine activity and therefore are widely used with fetal monitors. Tocotonometers measure the hardness of the abdomen wall, which is an indication of the uterine activity, by various mechanical means. Specifically, tocotonometers include strain gauge elements mounted to an elastic beam. Tocotonometers are expensive, structurally delicate, i.e., break easily, and are difficult to sanitize between uses. In use, the tocotonometer is held adjacent to the abdomen, usually by a belt-like device, in the vicinity of the fundus, i.e., the top of the uterus. The tocotonometer after pre-load by the belt responds with a constant recording level between contractions. The output of the tocotonometer is transmitted to the fetal monitor. Examples of such tocotonometers are manufactured by Huntleigh, Model #447, Corometrics, Model #2260 and Hewlett-Packard, Model #15248A. Other types of mechanical-type sensors for measuring uterine contractions are disclosed in U.S. Pat. Nos. 3,913,563; 4,949,730; 4,966,152 and 4,989,615. Like the tocotonometers, these devices are expensive, complicated in construction and use and difficult to sanitize between uses. The sensor disclosed in U.S. Pat. No. 4,949,730 utilizes a piezoelectric element which cannot measure contractions over a sustained period of time because the charge of the piezoelectric element dissipates quickly, say on the order of several seconds.
Accordingly, it is an object of the present invention to provide an apparatus and method for detecting uterine activity which is inexpensive, non-complicated in construction and easy to operate.
It is a further object of the present invention to provide an apparatus for detecting uterine activity which can be easily cleaned.
It is a further object of the present invention to provide an apparatus for detecting uterine activity which can be made disposable or reusable as required.
It is a further object of the present invention to provide an apparatus with a signal for detecting uterine activity which does not decay or electrically drift over time.
It is yet a further object of the present invention to provide an apparatus for detecting uterine activity which can be interchangeable with presently available fetal monitors.